Changes and trends of soil water resources under land use conversion in the loess tableland-gully region over the past 20 years

The loess tableland-gully region, China. The Grain for Green Program (GFGP) has been implemented on the Loess Plateau for over 20 years, and the changes of soil water resources are widely concerned. Based on measurements of soil water content (0–6 m) in 2003, 2011, and 2024, this study investigates the changing trend and recharge characteristics of soil water under different land uses. Soil water recharge depth reached to 2.4–2.6 m in forestlands, and 4.2–4.6 m in both wheat fields and grassland in a wet year with a 6-year return period. Soil water content (SWC) was consistently in a severe deficit status in the root zone below the recharge depth in forestland after 14 years old, but did not show a continuous decreasing trend, which reflected a balance between forest water consumption and precipitation infiltration. As the orchards were converted to cropland or grassland, the SWC gradually increased with rainfall infiltration and was back to be close to the field capacity in 3–6 m soil depths after 4–6 years. The GFGP has not caused a severe soil water crisis under a reasonable land use structure. The limited and variable precipitation should be maximally intercepted and infiltrated into the soil, so both the rainfed agricultural production and the forest-grassland vegetation can achieve sustainable development in the Loess Plateau under the carrying capacity of precipitation resources. • The SWC tends to stabilize instead of to decline in forestland older than 14 years. • The SWC increases after the orchard is converted back to cropland or grassland. • Rational land uses can ensure the sustainability of regional soil water resources.